The present invention relates to a wheel-acting force measuring device for detecting a road surface friction force, a normal counterforce and a road surface friction coefficient, which can be used as a component of either an antilock brake system (ABS) for preventing the locking of wheels on application of the hard brake to a vehicle or a traction control system for preventing excessive slippage of wheels during acceleration.
As for such wheel-acting force measuring device for detecting a load surface friction force, a normal counterforce and a road surface friction coefficient, which, can be used as a component of either an antilock brake system for vehicles or a traction control system, various types have heretofore been developed and proposed. However, such known devices require a relative-to-ground velocity sensor or a vehicle deceleration sensor to accurately find the vehicle velocity, making the device complicated and presenting a problem of accuracy. Thus, there has been a need for a device for directly measuring dynamic quantities concerning actions between the road surface and the wheels.
To meet this need, the present applicant proposed, in Japanese Patent Application No. Hei 3-130840, a wheel-acting force measuring device comprising a hole formed in or adjacent an axle, a stress sensor having a strain gauge attached thereto, said stress sensor being fixedly embedded in said hole with its strain gauge oriented in a suitable direction according to an intended stress or load, so that it is capable of directly measuring an optional stress or load occurring in or adjacent the axle.
However, there is a problem that detection signals delivered from the stress detecting sensor are influenced by cross talk according to the selected position of the hole since there are produced in or adjacent the axle a complicated shearing strain accompanying a bending deformation caused by a road surface friction force, a vertical stress and a side force acting on the wheel and a shearing strain accompanying a torsional deformation caused by the brake torque during application of the brake.